The present invention generally relates to radio frequency communications and more particularly to a radio frequency communication protocol between an interrogator and a tag.
Radio frequency (RF) tags are used for tracking of ground-based inventory by an overhead vehicle such as an aircraft or satellite. Upon interrogation by the radar of the aircraft or satellite, the radar responsive tag will transmit. a unique identifier. The unique identifier provides information about the tag. As such, RF tags are used to control inventory of assets on land and sea.
Typically, the RF tags are interrogated at unscheduled times. Accordingly, the RF tag must be turned on continuously to listen for the interrogator's signal. However, the tag's power consumption limits the tag's battery life to only a few hours when continuously listening for the interrogator. This deficiency is amplified by the fact that interrogation times are irregular and scheduling is impractical and/or impossible. The prior art RF tags typically remain in a state of readiness for interrogation thereby leading to a substantial amount of power consumption.
Prior art RF tags that allow unscheduled communications with an interrogator have limited signal processing and can only operate at short ranges. However, the limited signal processing ability of these prior art RF tags limits the tags to the processing of very strong signals. Weak and noisy signals are not useable with the prior art RF tag. This results in a limited operating range from as little as 1 meter to at most 100 meters for the prior art RF tag.
The present invention addresses the above-mentioned deficiencies in the prior art RF tags by providing a RF tag communications protocol between an interrogator and the RF tag. The communications protocol of the present invention provides a method whereby power consumption within the RF tag is adjusted thereby providing a power savings within the RF tag and extending the battery lifetime thereof. Additionally, the RF communications protocol of the present invention provides a method whereby the RF tag will respond only to an interrogator that is within a prescribed range. The RF communications protocol of the present invention provides a method of communication between an RF tag and an interrogator that is power efficient.